Dev Headers

Makes it easier to read Content-Security-Policy (CSP) and Permissions-Policy (PP) headers, and checks that all other related headers have been set for the HTML and linked resources (e.g. Referrer-Policy). It can also set a "X-Dev-Key" header on all requests to your server, where the value is typically kept as a secret, and allows your server to enable additional debug information (just as an extra precaution, your server should also check the source IP address, and ideally that you are logged in).